The overall objective is to determine morphological and correlated biological stages of tumorigenesis which can be reversed or arrested. Four critical models in inbred mice, developed by the applicant to represent a spectrum of human tumor types, are being studied: 1. Cervical carcinoma initiated by methylcholanthrene - promoting effect of Enovid. 2. Hodgkin's-like tumors of strain SJL/J - arrest by immunotherapy; role of genetic factors including the beige mutant genes. 3. Viral leukemogenesis - mechanisms of action of steel alleles in susceptibility. 4. Wx/Wv and Sl/Sld - single locus models for ovarian and pituitary tumorigenesis; correlation of morphological stages with pituitary hormone levels measured by radioimmunoassay. This group of models represents initiation by extrinsic carcinogens, intrinsic hormones, and viruses and promotion by extrinsic and intrinsic hormones, viruses, and as yet, unknown factors.